Continuous flow dryers are well known in the art and are available in a variety of designs, all generally including the following elements: (1) interior and exterior walls between which moist grain to be dried flows; (2) such moist grain being fed by an input means at the dryer top and flowing downwardly between the walls to a variable discharge means located substantially at the bottom of the dryer; (3) the interior walls partially defining a heat plenum into which hot air flows; (4) the interior and exterior walls each having numerous holes through which hot air from the heat plenum flows, which hot air is operative to reduce the moisture content of the grain flowing therebetween; and (5) the speed of the discharge means being variable such that the amount of time the grain drys, and thereby its final moisture content, is a function thereof.
The present invention is directed generally to a grain moisture sensor for use in determining the moisture content of grain and more specifically to a grain moisture sensor capable of determining grain moisture content and controlling the flow of grain in a continuous flow grain dryer by varying the speed of the variable discharge means such that the flow therein is regulated by the sensor, thereby allowing sufficient drying action to reduce the grain moisture content to a predetermined level, prior to being discharged therefrom.
The earliest electronic grain moisture testers were operated by direct current conductance. This method is accurate if moisture content is consistent throughout the kernel but rapid drying causes the outside of the kernel to be drier than the center, thereby providing inaccurate results.
There are also several known ways to measure grain moisture content by oven drying. The fastest of these methods, however, requires three hours and a grinding of the grain which are unacceptable for an on-line control system.
The Karl Fischer titration method is a chemical test which is specific for water. This is probably the most accurate moisture measurement method but it would likewise, not be practical for an on-line control system.
Microwave attenuation, while very accurate, is unsuitable because it is based on the dielectric loss factor which is not as consistent or well defined as the dielectric constant. Accordingly, expensive research would be required in order to develop a microwave based attenuation method.
Additionally, prior art teaches measurement of grain moisture content by measuring the temperature of the grain during the drying process, the moisture content of the grain being inferred from the grain temperature. This method, although simple, is not accurate due to the lack of a precise correlation between grain temperature and moisture content. This may result in grain which is overdry or underdry.
Another method taught by the prior art is to conduct the measurement in the discharge auger of the dryer. This method may be effective at determining the moisture content of the grain but the measurement is conducted at a point where it is too late to increase or decrease drying time as required. Consequently, it is more a means for grading the job done by the dryer than for affecting the proper drying.
Most electronic equipment used for measurement of moisture in grain is based on capacitance measurement. The capacitance of a given sensor depends on the dielectric constant of the grain in the sensor. Since the dielectric constant for grain is much lower than the dielectric constant for water, a small change in the amount of moisture in grain causes a relatively large change in its dielectric constant. This change in dielectric constant with grain moisture content makes it ideal for use in measuring moisture content and controlling drying equipment.
Accordingly, it is a primary objective of the present invention to provide an apparatus which is capable of making an accurate determination of grain moisture content.
Another objective of the present invention is to provide a means for controlling the flow of grain in a continuous flow dryer so as to effect the proper amount of drying required to attain a predetermined moisture content.
Another objective of the present invention is to provide a method for measuring grain moisture content and controlling grain flow such that the determination of moisture content is made at a point in the flow where the rate of flow may be varied to allow for more or less drying of the grain being tested, if the moisture content measured exceeds or falls short of the predetermined level.
Another objective of the present invention is to provide a grain moisture sensor which is simple and rugged in construction, easy to install and operate and which is efficient in operation.